Image formation is a procedure whereby a digital image is recreated on a medium by propelling droplets of ink or another type of print fluid onto a medium, such as paper, plastic, a substrate for 3D printing, etc. Image formation is commonly employed in apparatuses, such as printers (e.g., inkjet printer), facsimile machines, copying machines, plotting machines, multifunction peripherals, etc. The core of a typical jetting apparatus or image forming apparatus is one or more liquid-droplet ejection heads (referred to generally herein as “printheads”) having nozzles that discharge liquid droplets, a mechanism for moving the printhead and/or the medium in relation to one another, and a controller that controls how liquid is discharged from the individual nozzles of the printhead onto the medium in the form of pixels.
A typical printhead includes a plurality of nozzles aligned in one or more rows along a discharge surface of the printhead. Each nozzle is part of a “jetting channel”, which includes the nozzle, a pressure chamber, and an actuator, such as a piezoelectric actuator. A printhead also includes a drive circuit that controls when each individual jetting channel fires based on image data. To jet from a jetting channel, the drive circuit provides a jetting pulse to the actuator, which causes the actuator to deform a wall of the pressure chamber. The deformation of the pressure chamber creates pressure waves within the pressure chamber that eject a droplet of print fluid (e.g., ink) out of the nozzle.
In an attempt to reduce the size of printheads, the jetting channels within the printheads are moved closer together. Also, Drop on Demand (DoD) printing is moving towards higher productivity and quality, which requires small droplet sizes ejected at high jetting frequencies. The print quality delivered by a printhead depends on ejection or jetting characteristics, such as droplet velocity, droplet mass (or volume/diameter), jetting direction, etc. Temperature of a printhead or the print fluid in the printhead may affect the jetting characteristics. It is therefore desirable to detect temperature variations across a printhead to achieve high quality printing. One way to detect temperature in a printhead is to embed a temperature sensor, such as a thermistor or a thermocouple, in a body of the printhead. Although the use of temperature sensors may be effective in some circumstances, the use of temperature sensors adds additional parts to printheads that are subject to failure, and adds additional cost to the printheads.